1. Field of the Invention
The present invention relates to a technical field involving a driver of a liquid crystal panel of a matrix driving type which adopts transistor driving, metal-insulator-metal (MIM) driving, or the like, and a liquid crystal device and electronic equipment using this driver. More particularly, this invention is concerned with a technical field involving a driver for driving a liquid crystal panel so that images of different aspect ratios can be displayed according to the type of an image signal, a liquid crystal device and electronic equipment using this driver.
2. Description of Related Art
In recent years, liquid crystal devices have been requested to cope with a plurality of different specifications for display in compliance with the demands from markets for displaying a TV picture in a wider screen and for sharing the same specifications for display with computers or the like. However, a dot-matrix type liquid crystal device in accordance with a related art has difficulty in handling a non-image display area in which no picture is displayed and which is produced when corresponding a plurality of specifications for display having different aspect ratios. For example, when an attempt is made to display a screen of an aspect ratio 4:3, which conforms to an existing National Television System Committee (NTSC) standard and a Phase Alternation Line (PAL) standard, being involved in a dot-matrix type liquid crystal device offering a screen of an aspect ratio 16:9 which conforms to a recent high-definition TV standard and an NTSC standard on a wide screen, non-image display areas are created on the right and left sides of the image display field. The non-image display areas are normally blackened. However, when an ordinary shift register is driven for blackening, it is impossible to horizontally scan all pixel electrodes included in the non-image display areas and display them within each horizontal retrace period. Consequently, long adopted is the technique of adjusting the line frequency for a horizontal scan using an external storage device such as a line memory, or the technique of driving a shift register only in the non-image display areas at a high frequency that is 1.5 times to twice higher than the frequency driven in the image display area.
In contrast, when an attempt is made to display a screen with an aspect ratio 16:9 based on the high-definition TV standard or the like in a dot-matrix type liquid crystal device offering a screen with an aspect ratio 4:3 based on the existing NTSC standard or the like, non-image display areas are created above and below the image display area. The non-image display areas are normally blackened. Even in this case, long adopted is the technique of adjusting a line frequency for vertical scanning using an external storage device, or the technique of driving a shift register only in the non-image display areas at a frequency which is higher than the frequency driven in the image display area.
Moreover, Japanese Unexamined Patent Publication No. 9-154086 has disclosed a display device including a device for controlling the horizontal scan so that a signal sent from a sub-video signal processor can be displayed in right and left non-image display areas at the same time. According to this art, since pixels constituting the right and left non-image display areas are scanned at the same time, the time required for scanning the areas is halved.
However, when the foregoing system of driving a shift register, at a frequency higher than the frequency at which the shift register is driven in an image display area is adopted in order to blacken non-image display areas, the shift register must exhibit excellent characteristics. Moreover, there is a problem that since the time required for selecting any pixels in the non-image display areas is shortened, a sufficient contrast ratio cannot be attained. In addition, since the driving frequency becomes high, the power consumption increases. On the other hand, the foregoing system using an external storage device such as a line memory has a problem that not only an increase in cost is invited, but also the design of peripheral circuits or the operational control gets more complex.
According to the art disclosed in Japanese Unexamined Patent Publication No. 9-154086, in order that the pixels constituting the right and left non-image display areas are scanned concurrently, complex circuits such as a sub-video signal processor and video signal switching device must be incorporated in the drive circuit. This makes the configuration of a display device or a control complex. Furthermore, for blackening the right and left non-image display areas, the scan time that is approximately one-half of the scan time required for scanning the pixels in the right and left non-image display areas separately is required.